Light detection systems are being increasingly utilized in a wide variety of applications.
In one such light detection system, Light Imaging Detecting And Ranging (LIDAR) scanning, a scanner launches a laser beam that scans across a scene that encompasses a target object and measures light reflected back from a large number of points that lie on surfaces visible in the scene. Each scan point from which reflected light is received by the scanning system has a measured location in three dimensional (3D) space, to within some measurement error, that typically is recorded relative to a point (x,y,z) in the local coordinate system of the scanner. LIDAR systems are described, for example, in U.S. Pat. No. 5,988,862, issued Nov. 3, 1999, titled “INTEGRATED SYSTEM FOR QUICKLY AND ACCURATELY IMAGING AND MODELING THREE DIMENSIONAL OBJECTS,” which is hereby incorporated herein by reference in its entirety to provide background information regarding the present invention.
In a light detection system, such as the LIDAR scanning system referenced above, the intensity of the return light from a target is typically not known in advance of receiving the light. As a consequence, the light return system must be able to determine the range of return light intensity using as wide a variety of return powers as possible; that is, the system must have as wide a dynamic range as possible. Current light detection systems are able to range with sufficient accuracy on a variety of expected target surfaces and ranges. However, there exist some exceptional so-called cooperative targets, e.g., surveying prisms, that return thousands of times more light than typical non-cooperative targets such as walls, pipes and rock. The light detection techniques provided by the present invention allow a light detection system to duplicate the dynamic range of the low intensity, non-cooperative targets for high intensity cooperative targets. Both dynamic ranges of return pulse light are supported at the same time so that no apriori knowledge of the target is required to accurately range.
In accordance with the invention, one or two beam splitters are utilized to reduce the intensity of reflected light that is received from a high intensity source to levels that can be accurately ranged. The beam splitter system increases the effective dynamic range of the detection and ranging system passively without any need to reconfigure the system.